Gas turbine engine airfoil

ABSTRACT

An airfoil for a turbine engine includes an airfoil that has pressure and suction sides that extend in a radial direction from a 0% span position at an inner flow path location to a 100% span position at an airfoil tip. The airfoil has a curve that corresponds to a relationship between a trailing edge sweep angle and a span position. The trailing edge sweep angle is in a range of 10° to 20° in a range of 40-70% span position, and the trailing edge sweep angle is positive from 0% span to at least 95% span. The airfoil has a relationship between a leading edge dihedral and a span position. The leading edge dihedral is negative from the 0% span position to the 100% span position. A positive dihedral corresponds to suction side-leaning, and a negative dihedral corresponds to pressure side-leaning.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.61/942,026, which was filed on Feb. 19, 2014 and is incorporated hereinby reference.

BACKGROUND

This disclosure relates generally to an airfoil for gas turbine engines,and more particularly to a fan or compressor blade and the relationshipbetween the blade's aerodynamic leading edge sweep and aerodynamicleading edge dihedral.

A turbine engine such as a gas turbine engine typically includes a fansection, a compressor section, a combustor section and a turbinesection. Air entering the compressor section is compressed and deliveredinto the combustor section where it is mixed with fuel and ignited togenerate a high-speed exhaust gas flow. The high-speed exhaust gas flowexpands through the turbine section to drive the compressor and the fansection. The compressor section typically includes low and high pressurecompressors, and the turbine section includes low and high pressureturbines.

The propulsive efficiency of a gas turbine engine depends on manydifferent factors, such as the design of the engine and the resultingperformance debits on the fan that propels the engine. As an example,the fan may rotate at a high rate of speed such that air passes over thefan airfoils at transonic or supersonic speeds. The fast-moving aircreates flow discontinuities or shocks that result in irreversiblepropulsive losses. Additionally, physical interaction between the fanand the air causes downstream turbulence and further losses. Althoughsome basic principles behind such losses are understood, identifying andchanging appropriate design factors to reduce such losses for a givenengine architecture has proven to be a complex and elusive task.

SUMMARY

In one exemplary embodiment, an airfoil for a turbine engine includes anairfoil that has pressure and suction sides that extend in a radialdirection from a 0% span position at an inner flow path location to a100% span position at an airfoil tip. The airfoil has a curve thatcorresponds to a relationship between a trailing edge sweep angle and aspan position. The trailing edge sweep angle is in a range of 10° to 20°in a range of 40-70% span position, and the trailing edge sweep angle ispositive from 0% span to at least 95% span. The airfoil has arelationship between a leading edge dihedral and a span position. Theleading edge dihedral is negative from the 0% span position to the 100%span position. A positive dihedral corresponds to suction side-leaning,and a negative dihedral corresponds to pressure side-leaning.

In a further embodiment of the above, the trailing edge sweep angle isin a range of 10° to 20° in a range of 50-70% span position.

In a further embodiment of any of the above, the trailing edge sweepangle is in a range of 10° to 20° in a range of 60-70% span position.

In a further embodiment of any of the above, the trailing edge sweepangle is positive from 0%-95% span.

In a further embodiment of any of the above, the trailing edge sweepangle transitions from less positive to more positive at greater than an80% span position.

In a further embodiment of any of the above, a positive-most trailingedge sweep angle is at a greater than 50% span position.

In a further embodiment of any of the above, a positive-most trailingedge sweep angle is at about a 70% span position.

In a further embodiment of any of the above, a trailing edge sweep angleis within 5° along a portion of the curve from the 0% span position to a60% span position.

In a further embodiment of any of the above, a positive-most trailingedge sweep angle lies along the portion.

In a further embodiment of any of the above, a positive-most trailingedge sweep angle is within the range of 10° to 20° in the range of40-70% span position.

In a further embodiment of any of the above, the airfoil has a leadingedge sweep angle curve that corresponds to a relationship between aleading edge sweep angle and a span position. A leading edge sweep angleat the 100% span position is less negative than a forward-most leadingedge sweep angle along the curve. The curve has a decreasing leadingedge sweep angle rate in a range of a 80-100% span position.

In a further embodiment of any of the above, the leading edge sweepangle curve has a portion that extends span-wise toward the tip and fromthe forward-most leading edge sweep angle. The portion has a decreasingleading edge sweep angle that crosses a zero sweep angle in the range ofa 30-40% span position.

In a further embodiment of any of the above, the forward-most leadingedge sweep angle is in a range of −10° to −15°.

In a further embodiment of any of the above, the forward-most leadingedge sweep angle is about −10°.

In a further embodiment of any of the above, a rearward-most leadingedge sweep angle is in a range of 15° to 30°.

In a further embodiment of any of the above, a leading edge sweep angleat the 0% span position and a leading edge sweep angle at the 100% spanposition are within 5° of one another.

In a further embodiment of any of the above, a leading edge sweep angleat the 0% span position is negative, and a leading edge sweep angle atthe 100% span position is positive.

In a further embodiment of any of the above, the leading edge sweepangle at the 0% span position is positive. The leading edge sweep angleat the 100% span position is negative.

In a further embodiment of any of the above, the leading edge dihedralat the 0% span position is in the range of −3° to −12°.

In a further embodiment of any of the above, the leading edge dihedralat the 0% span position is about −4°.

In a further embodiment of any of the above, the leading edge dihedralat the 0% span position is about −10°.

In a further embodiment of any of the above, the leading edge dihedralextends from the 0% span position to a 20% span position and has aleading edge dihedral in a range of −2° to −6°.

In a further embodiment of any of the above, the leading edge dihedralincludes a first point at a 75% span position and extends generallylinearly from the first point to a second point at the 85% spanposition.

In a further embodiment of any of the above, a maximum negative dihedralis in a range of 95-100% span position.

In a further embodiment of any of the above, a least negative dihedralis in a range of 5-15% span position.

In a further embodiment of any of the above, a maximum negative dihedralis in a range of 65-75% span position.

In a further embodiment of any of the above, a least negative dihedralis in a range of 0-10% span position.

In a further embodiment of any of the above, a maximum negative dihedralis in a range of 50-60% span position.

In a further embodiment of any of the above, the airfoil is a fan bladefor a gas turbine engine.

In a further embodiment of any of the above, the airfoil has arelationship between a trailing edge dihedral and a span position. Thetrailing edge dihedral is positive from the 0% span position to the 100%span position. A positive dihedral corresponds to suction side-leaningand a negative dihedral corresponds to pressure side-leaning.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure can be further understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings wherein:

FIG. 1 schematically illustrates a gas turbine engine embodiment.

FIG. 2A is a perspective view of a portion of a fan section.

FIG. 2B is a schematic cross-sectional view of the fan section.

FIG. 2C is a cross-sectional view a fan blade taken along line 2C-2C inFIG. 2B.

FIG. 3A is a schematic view of fan blade span positions for an airfoilwithout any curvature at the leading and trailing edges.

FIG. 3B is an elevational view of a fan blade airfoil illustratingvelocity vectors in relation to the leading and trailing edges.

FIG. 3C is a schematic perspective view of an airfoil fragmentillustrating the definition of a leading edge sweep angle.

FIG. 3D is a schematic perspective view of an airfoil fragmentillustrating the definition of a trailing edge sweep angle.

FIG. 4 is a schematic representation of a dihedral angle for an airfoil.

FIG. 5A graphically illustrates a leading edge sweep angle relative to aspan position for a set of first example airfoils and a prior artairfoil.

FIG. 5B graphically illustrates a trailing edge sweep angle relative toa span position for a set of first example airfoils and a prior artairfoil.

FIG. 6A graphically illustrates a leading edge sweep angle relative to aspan position for a set of second example airfoils and the prior artairfoil.

FIG. 6B graphically illustrates a trailing edge sweep angle relative toa span position for a set of second example airfoils and the prior artairfoil.

FIG. 7A illustrates a relationship between a leading edge aerodynamicdihedral angle and a span position for the set of first example airfoilsand a prior art curve.

FIG. 7B illustrates a relationship between a trailing edge aerodynamicdihedral angle and a span position for the set of first example airfoilsand a prior art curve.

FIG. 8A illustrates a relationship between a leading edge aerodynamicdihedral angle and a span position for the set of second exampleairfoils and the prior art curve.

FIG. 8B illustrates a relationship between a trailing edge aerodynamicdihedral angle and a span position for the set of second exampleairfoils and the prior art curve.

The embodiments, examples and alternatives of the preceding paragraphs,the claims, or the following description and drawings, including any oftheir various aspects or respective individual features, may be takenindependently or in any combination. Features described in connectionwith one embodiment are applicable to all embodiments, unless suchfeatures are incompatible.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool turbofan thatgenerally incorporates a fan section 22, a compressor section 24, acombustor section 26 and a turbine section 28. Alternative engines mightinclude an augmenter section (not shown) among other systems orfeatures. The fan section 22 drives air along a bypass flow path B in abypass duct defined within a nacelle 15, while the compressor section 24drives air along a core flow path C for compression and communicationinto the combustor section 26 then expansion through the turbine section28. Although depicted as a two-spool turbofan gas turbine engine in thedisclosed non-limiting embodiment, it should be understood that theconcepts described herein are not limited to use with two-spoolturbofans as the teachings may be applied to other types of turbineengines including three-spool architectures. That is, the disclosedairfoils may be used for engine configurations such as, for example,direct fan drives, or two- or three-spool engines with a speed changemechanism coupling the fan with a compressor or a turbine sections.

The exemplary engine 20 generally includes a low speed spool 30 and ahigh speed spool 32 mounted for rotation about an engine centrallongitudinal axis X relative to an engine static structure 36 viaseveral bearing systems 38. It should be understood that various bearingsystems 38 at various locations may alternatively or additionally beprovided, and the location of bearing systems 38 may be varied asappropriate to the application.

The low speed spool 30 generally includes an inner shaft 40 thatinterconnects a fan 42, a first (or low) pressure compressor 44 and afirst (or low) pressure turbine 46. The inner shaft 40 is connected tothe fan 42 through a speed change mechanism, which in exemplary gasturbine engine 20 is illustrated as a geared architecture 48 to drivethe fan 42 at a lower speed than the low speed spool 30. The high speedspool 32 includes an outer shaft 50 that interconnects a second (orhigh) pressure compressor 52 and a second (or high) pressure turbine 54.A combustor 56 is arranged in exemplary gas turbine 20 between the highpressure compressor 52 and the high pressure turbine 54. A mid-turbineframe 57 of the engine static structure 36 is arranged generally betweenthe high pressure turbine 54 and the low pressure turbine 46. Themid-turbine frame 57 further supports bearing systems 38 in the turbinesection 28. The inner shaft 40 and the outer shaft 50 are concentric androtate via bearing systems 38 about the engine central longitudinal axisX which is collinear with their longitudinal axes.

The core airflow is compressed by the low pressure compressor 44 thenthe high pressure compressor 52, mixed and burned with fuel in thecombustor 56, then expanded over the high pressure turbine 54 and lowpressure turbine 46. The mid-turbine frame 57 includes airfoils 59 whichare in the core airflow path C. The turbines 46, 54 rotationally drivethe respective low speed spool 30 and high speed spool 32 in response tothe expansion. It will be appreciated that each of the positions of thefan section 22, compressor section 24, combustor section 26, turbinesection 28, and fan drive gear system 48 may be varied. For example,gear system 48 may be located aft of combustor section 26 or even aft ofturbine section 28, and fan section 22 may be positioned forward or aftof the location of gear system 48.

The engine 20 in one example is a high-bypass geared aircraft engine. Ina further example, the engine 20 bypass ratio is greater than about six(6), with an example embodiment being greater than about ten (10), thegeared architecture 48 is an epicyclic gear train, such as a planetarygear system or other gear system, with a gear reduction ratio of greaterthan about 2.3 and the low pressure turbine 46 has a pressure ratio thatis greater than about five. In one disclosed embodiment, the engine 20bypass ratio is greater than about ten (10:1), the fan diameter issignificantly larger than that of the low pressure compressor 44, andthe low pressure turbine 46 has a pressure ratio that is greater thanabout five (5:1). Low pressure turbine 46 pressure ratio is pressuremeasured prior to inlet of low pressure turbine 46 as related to thepressure at the outlet of the low pressure turbine 46 prior to anexhaust nozzle. The geared architecture 48 may be an epicyclic geartrain, such as a planetary gear system or other gear system, with a gearreduction ratio of greater than about 2.3:1. It should be understood,however, that the above parameters are only exemplary of one embodimentof a geared architecture engine and that the present invention isapplicable to other gas turbine engines including direct driveturbofans.

The example gas turbine engine includes the fan 42 that comprises in onenon-limiting embodiment less than about twenty-six (26) fan blades. Inanother non-limiting embodiment, the fan section 22 includes less thanabout twenty (20) fan blades. Moreover, in one disclosed embodiment thelow pressure turbine 46 includes no more than about six (6) turbinerotors schematically indicated at 34. In another non-limiting exampleembodiment the low pressure turbine 46 includes about three (3) turbinerotors. A ratio between the number of fan blades 42 and the number oflow pressure turbine rotors is between about 3.3 and about 8.6. Theexample low pressure turbine 46 provides the driving power to rotate thefan section 22 and therefore the relationship between the number ofturbine rotors 34 in the low pressure turbine 46 and the number ofblades 42 in the fan section 22 disclose an example gas turbine engine20 with increased power transfer efficiency.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft, withthe engine at its best fuel consumption—also known as “bucket cruiseThrust Specific Fuel Consumption (‘TSFCT’)”—is the industry standardparameter of lbm of fuel being burned divided by lbf of thrust theengine produces at that minimum point. “Low fan pressure ratio” is thepressure ratio across the fan blade alone, without a Fan Exit Guide Vane(“FEGV”) system. The low fan pressure ratio as disclosed hereinaccording to one non-limiting embodiment is less than about 1.55. Inanother non-limiting embodiment the low fan pressure ratio is less thanabout 1.45. In another non-limiting embodiment the low fan pressureratio is from 1.1 to 1.45. “Low corrected fan tip speed” is the actualfan tip speed in ft/sec divided by an industry standard temperaturecorrection of [(Tram° R)/(518.7° R)]^(0.5). The “low corrected fan tipspeed” as disclosed herein according to another non-limiting embodimentis less than about 1200 ft/second.

Referring to FIG. 2A-2C, the fan blade 42 is supported by a fan hub 60that is rotatable about the axis X. Each fan blade 42 includes anairfoil 64 extending in a radial span direction R from a root 62 to atip 66. A 0% span position corresponds to a section of the airfoil 64 atthe inner flow path (e.g., a platform), and a 100% span positioncorresponds to a section of the airfoil 64 at the tip 66.

The root 62 is received in a correspondingly shaped slot in the fan hub60. The airfoil 64 extends radially outward of the platform, whichprovides the inner flow path. The platform may be integral with the fanblade or separately secured to the fan hub, for example. A spinner 66 issupported relative to the fan hub 60 to provide an aerodynamic innerflow path into the fan section 22.

The airfoil 64 has an exterior surface 76 providing a contour thatextends from a leading edge 68 aftward in a chord-wise direction H to atrailing edge 70, as shown in FIG. 2C. Pressure and suction sides 72, 74join one another at the leading and trailing edges 68, 70 and are spacedapart from one another in an airfoil thickness direction T. An array ofthe fan blades 42 are positioned about the axis X in a circumferentialor tangential direction Y. Any suitable number of fan blades may be usedin a given application.

The exterior surface 76 of the airfoil 64 generates lift based upon itsgeometry and directs flow along the core flow path C. The fan blade 42may be constructed from a composite material, or an aluminum alloy ortitanium alloy, or a combination of one or more of these.Abrasion-resistant coatings or other protective coatings may be appliedto the fan blade 42. The curves and associated values assume a fan in ahot, running condition (typically cruise).

One characteristic of fan blade performance relates to the fan blade'sleading and trailing edge sweep angles relative to a particular spanposition (R direction). Referring to FIG. 3A, span positions aschematically illustrated from 0% to 100% in 10% increments. Eachsection at a given span position is provided by a conical cut thatcorresponds to the shape of the core flow path, as shown by the largedashed lines. In the case of a fan blade with an integral platform, the0% span position corresponds to the radially innermost location wherethe airfoil meets the fillet joining the airfoil to the platform. In thecase of a fan blade without an integral platform, the 0% span positioncorresponds to the radially innermost location where the discreteplatform meets the exterior surface of the airfoil. In addition tovarying with span, leading and trailing edge sweep varies between a hot,running condition and a cold, static (“on the bench”) condition.

The axial velocity Vx (FIG. 3B) of the core flow C is substantiallyconstant across the radius of the flowpath. However the linear velocityU of a rotating airfoil increases with increasing radius. Accordingly,the relative velocity Vr of the working medium at the airfoil leadingedge increases with increasing radius, and at high enough rotationalspeeds, the airfoil experiences supersonic working medium flowvelocities in the vicinity of its tip. The relative velocity at theleading edge 68 is indicated as Vr_(LE), and the relative velocity atthe trailing edge 70 is indicated as Vr_(TE).

Supersonic flow over an airfoil, while beneficial for maximizing thepressurization of the working medium, has the undesirable effect ofreducing fan efficiency by introducing losses in the working medium'stotal pressure. Therefore, it is typical to sweep the airfoil's leadingedge over at least a portion of the blade span so that the workingmedium velocity component in the chordwise direction (perpendicular tothe leading edge) is subsonic. Since the relative velocity Vr increaseswith increasing radius, the sweep angle typically increases withincreasing radius as well. As shown in FIGS. 3C and 3D, the sweep angleσ at any arbitrary radius Rd (FIG. 3A) at the leading edge 68 isindicated as σ_(LE), and at the trailing edge 70, σ_(TE).

Referring to FIG. 3C, the leading edge sweep angle σ_(LE) is the acuteangle between a line 90 tangent to the leading edge 68 of the airfoil 64and a plane 92 perpendicular to the relative velocity vector Vr_(LE).The sweep angle is measured in plane 94, which contains both therelative velocity vector Vr_(LE) and the tangent line 90 and isperpendicular to plane 92. FIGS. 5A and 6A are provided in conformancewith this definition of the leading edge sweep angle σ_(LE).

Referring to FIG. 3D, the trailing edge sweep angle a is the acute anglebetween a line 96 tangent to the trailing edge 70 of the airfoil 64 anda plane 98 perpendicular to the relative velocity vector Vr_(TE). Thesweep angle is measured in plane 100, which contains both the relativevelocity vector Vr_(TE) and the tangent line 96 and is perpendicular toplane 98. FIGS. 5B and 6B are provided in conformance with thisdefinition of the trailing edge sweep angle σ_(TE).

Thus, a negative sweep angle indicates an airfoil edge locally orientedin a direction opposite the velocity vector (Vr_(LE) or Vr_(TE)), and apositive sweep angle indicates an airfoil edge locally oriented in thesame direction as the velocity vector.

An aerodynamic dihedral angle D (simply referred to as “dihedral”) isschematically illustrated in FIG. 4 for a simple airfoil. Anaxisymmetric stream surface S passes through the airfoil 64 at alocation that corresponds to a span location (FIG. 3A). For the sake ofsimplicity, the dihedral D relates to the angle at which a line L alongthe leading or trailing edge tilts with respect to the stream surface S.A plane P is normal to the line L and forms an angle with the tangentialdirection Y, providing the dihedral D. A positive dihedral D correspondsto the line tilting toward the suction side (suction side-leaning), anda negative dihedral D corresponds to the line tilting toward thepressure side (pressure side-leaning). The method of determining andcalculating the dihedral for more complex airfoil geometries isdisclosed in Smith Jr., Leroy H., and Yeh, Hsuan “Sweep and DihedralEffects in Axial-Flow Turbomachinery.” J. Basic Eng. Vol. 85 Iss. 3, pp.401-414 (Sep. 1, 1963), which is incorporated by reference in itsentirety. Leading and trailing edge dihedral, like sweep, varies betweena hot, running condition and a cold, static (“on the bench”) condition.

Several example fan blades are shown in each of the graphs in FIGS.5A-6B, each blade represented by a curve. Only one curve in each graphis discussed for simplicity. Referring to FIGS. 5A and 6A, the airfoilhas a curve corresponding to a relationship between a leading edge sweepangle (LE SWEEP) and a span position (LE SPAN %). The curves illustratethat a leading edge sweep angle at the 100% span position (116 in FIG.5A; 128 in FIG. 6A) is less negative than a forward-most leading edgesweep angle (112 in FIG. 5A; 124 in FIG. 6A) along the curve. The curveshave a decreasing leading edge sweep angle rate (108 in FIG. 5A; 118 inFIG. 6A) in a range of a 80-100% span position. That is, the sweep angleis not constant, but changes. This change, or leading edge sweep anglerate, decreases in the range of 80-100% span.

The curves have a portion extending span-wise toward the tip and fromthe forward-most leading edge sweep angle (112 in FIG. 5A; 124 in FIG.6A). The forward-most leading edge sweep angle is in a range of −10° to−15°. In the examples shown in FIGS. 5A and 6A, the forward-most leadingedge sweep angle is about −10°. The portion has a decreasing leadingedge sweep angle that crosses a zero sweep angle (106 in FIG. 5A; 120 inFIG. 6A) in the range of a 30-40% span position.

A rearward-most leading edge sweep angle (114 in FIG. 5A; 126 in FIG.6A) is in a range of 15° to 30°. In the example shown in FIG. 5A, therearward-most leading edge sweep angle 114 is in a range of 75-85% spanposition. With continuing reference to FIG. 5A, a leading edge sweepangle 110 at the 0% span position and the leading edge sweep angle 116at the 100% span position are within 5° of one another. Both the leadingedge sweep angle at the 0% span position and the leading edge sweepangle at the 100% span position are positive.

Referring to FIG. 6A, a leading edge sweep angle 122 at the 0% spanposition is negative, and a leading edge sweep angle 128 at the 100%span position is positive. The leading edge sweep angle 128 at the 0%span position and the leading edge sweep angle 128 at the 100% spanposition are within 10° of one another.

Trailing edge sweep angles are graphically illustrated in FIGS. 5B and6B. The airfoil has curves corresponding to a relationship between atrailing edge sweep angle and the span position. Within a region of thecurve (142 in FIG. 5B; 150 in FIG. 6B), the trailing edge sweep angle(TE SWEEP) is in a range of 10° to 20° in a range of 40-70% spanposition (TE SPAN %). The trailing edge sweep angle is positive from 0%span to at least 95% span. In one example, the trailing edge sweep angleis in a range of 10° to 20° in a range of 50-70% span position, and inanother example, the trailing edge sweep angle is in a range of 10° to20° in a range of 60-70% span position. Within the 60-70% span position,the trailing edge sweep angle is about 15°. In the examples, apositive-most trailing edge sweep angle (144 in FIG. 5B; 152 in FIG. 6B)is within the range of 10° to 20° in the range of 40-70% span position.

Referring to FIG. 5B, the trailing edge sweep angle is positive from0%-95% span. The trailing edge sweep angle 146 at the 100% span positionis about zero, but negative. The trailing edge sweep angle transitionsfrom less positive to more positive at greater than an 80% span positionat point 148. The positive-most trailing edge sweep angle 144 is at agreater than 50% span position.

Referring to FIG. 5B, a trailing edge sweep angle 154 at the 0% spanposition and a trailing edge sweep angle 156 at the 100% span positionare about the same. The positive-most trailing edge sweep angle 152 isat about a 70% span position.

The leading and trailing edge sweep in a hot, running condition alongthe span of the airfoils 64 relate to the contour of the airfoil andprovide necessary fan operation in cruise at the lower, preferentialspeeds enabled by the geared architecture 48 in order to enhanceaerodynamic functionality and thermal efficiency. As used herein, thehot, running condition is the condition during cruise of the gas turbineengine 20. For example, the leading and trailing edge sweep in the hot,running condition can be determined in a known manner using numericalanalysis, such as finite element analysis. Example relationships betweenthe leading edge dihedral (LE DIHEDRAL) and the span position (LE SPAN%) are shown in FIGS. 7A and 8A for several example fan blades, eachrepresented by a curve. Only one curve in each graph is discussed forsimplicity. In the examples, the leading edge dihedral is negative fromthe 0% span position to the 100% span position.

The leading edge dihedral at the 0% span position (192 in FIG. 7A; 204in FIG. 8A) is in the range of −3° to −12°. In the examples shown inFIGS. 7A and 8A, the leading edge dihedral at the 0% span position isabout −4°.

The leading edge dihedral extends from the 0% span position to a 20%span position (196 in FIG. 7A; 208 in FIG. 8A) having a leading edgedihedral in a range of −2° to −6°.

In the examples shown in FIGS. 7A and 8A, the leading edge dihedralincludes a first point (200 in FIG. 7A; 210 in FIG. 8A) at a 75% spanposition and extends generally linearly from the first point to a secondpoint (202 in FIG. 7A; 214 in FIG. 8A) at the 85% span position. Thefirst point is in a range of −8° to −10° dihedral, and the second pointis in a range of −3° to −6° dihedral.

Referring to FIG. 7A, a maximum negative dihedral 198 is in a range of95-100% span position. A least negative dihedral 194 is in a range of5-15% span position. Referring to FIG. 8A, a maximum negative dihedral210 is in a range of 65-75% span position. A least negative dihedral 206is in a range of 0-10% span position.

Example relationships between the trailing edge dihedral and the spanposition are shown in FIGS. 7B and 8B for several example fan blades,each represented by a curve. Only one curve in each graph is discussedfor simplicity. In the examples, the trailing edge dihedral is positivefrom the 0% span position to the 100% span position. The relationshipprovides a generally C-shaped curve from the 0% span position to a 50%span position and then a 90% span position.

A trailing edge dihedral (230 in FIG. 7B; 240 in FIG. 8B) at the 0% spanposition is in a range of 20° to 25°. A trailing edge dihedral (232 inFIG. 7B; 242 in FIG. 8B) at about the 50% span position is in a range of2° to 6°. A trailing edge dihedral (237 in FIG. 7B; 247 in FIG. 8B) atthe 90% span position is in a range of 16° to 22°. From a 65% spanposition (234 in FIG. 7B; 244 in FIG. 8B) to a 75% span position (236 inFIG. 7B; 246 in FIG. 8B) the trailing edge dihedral increases about 5°.

A positive-most trailing edge dihedral (238 in FIG. 7B; 248 in FIG. 8B)in a 80%-100% span position is within 5° of the trailing edge dihedralin the 0% span position (230 in FIG. 7B; 240 in FIG. 8B). A leastpositive trailing edge dihedral (232 in FIG. 7B; 242 in FIG. 8B) is in a40%-55% span position.

The leading and trailing edge aerodynamic dihedral angle in a hot,running condition along the span of the airfoils 64 relate to thecontour of the airfoil and provide necessary fan operation in cruise atthe lower, preferential speeds enabled by the geared architecture 48 inorder to enhance aerodynamic functionality and thermal efficiency. Asused herein, the hot, running condition is the condition during cruiseof the gas turbine engine 20. For example, the leading and trailing edgeaerodynamic dihedral angle in the hot, running condition can bedetermined in a known manner using numerical analysis, such as finiteelement analysis. It should also be understood that although aparticular component arrangement is disclosed in the illustratedembodiment, other arrangements will benefit herefrom. Althoughparticular step sequences are shown, described, and claimed, it shouldbe understood that steps may be performed in any order, separated orcombined unless otherwise indicated and will still benefit from thepresent invention.

Although the different examples have specific components shown in theillustrations, embodiments of this invention are not limited to thoseparticular combinations. It is possible to use some of the components orfeatures from one of the examples in combination with features orcomponents from another one of the examples.

Although an example embodiment has been disclosed, a worker of ordinaryskill in this art would recognize that certain modifications would comewithin the scope of the claims. For that reason, the following claimsshould be studied to determine their true scope and content.

What is claimed is:
 1. An airfoil for a turbine engine comprising: anairfoil having pressure and suction sides extending in a radialdirection from a 0% span position at an inner flow path location to a100% span position at an airfoil tip, wherein the airfoil has a curvecorresponding to a relationship between a trailing edge sweep angle anda span position, wherein the trailing edge sweep angle is in a range of10° to 20° in a range of 40-70% span position, and the trailing edgesweep angle is positive from 0% span to at least 95% span, wherein theairfoil has a relationship between a leading edge dihedral and a spanposition, the leading edge dihedral negative from the 0% span positionto the 100% span position, wherein a positive dihedral corresponds tosuction side-leaning, and a negative dihedral corresponds to pressureside-leaning.
 2. The airfoil according to claim 1, wherein the trailingedge sweep angle is in a range of 10° to 20° in a range of 50-70% spanposition.
 3. The airfoil according to claim 2, wherein the trailing edgesweep angle is in a range of 10° to 20° in a range of 60-70% spanposition.
 4. The airfoil according to claim 1, wherein the trailing edgesweep angle is positive from 0%-95% span.
 5. The airfoil according toclaim 4, wherein the trailing edge sweep angle transitions from lesspositive to more positive at greater than an 80% span position.
 6. Theairfoil according to claim 4, wherein a positive-most trailing edgesweep angle is at a greater than 50% span position.
 7. The airfoilaccording to claim 1, wherein a positive-most trailing edge sweep angleis at about a 70% span position.
 8. The airfoil according to claim 1,wherein a trailing edge sweep angle is within 5° along a portion of thecurve from the 0% span position to a 60% span position.
 9. The airfoilaccording to claim 8, wherein a positive-most trailing edge sweep anglelies along the portion.
 10. The airfoil according to claim 1, wherein apositive-most trailing edge sweep angle is within the range of 10° to20° in the range of 40-70% span position.
 11. The airfoil according toclaim 1, wherein the airfoil has a leading edge sweep angle curvecorresponding to a relationship between a leading edge sweep angle and aspan position, wherein a leading edge sweep angle at the 100% spanposition is less negative than a forward-most leading edge sweep anglealong the curve, and wherein the curve has a decreasing leading edgesweep angle rate in a range of a 80-100% span position.
 12. The airfoilaccording to claim 11, wherein the leading edge sweep angle curve has aportion extending span-wise toward the tip and from the forward-mostleading edge sweep angle, the portion has a decreasing leading edgesweep angle that crosses a zero sweep angle in the range of a 30-40%span position.
 13. The airfoil according to claim 12, wherein theforward-most leading edge sweep angle is in a range of −10° to −15°. 14.The airfoil according to claim 13, wherein the forward-most leading edgesweep angle is about −10°.
 15. The airfoil according to claim 13,wherein a rearward-most leading edge sweep angle is in a range of 15° to30°.
 16. The airfoil according to claim 13, wherein a leading edge sweepangle at the 0% span position and a leading edge sweep angle at the 100%span position are within 5° of one another.
 17. The airfoil according toclaim 13, wherein a leading edge sweep angle at the 0% span position isnegative, and a leading edge sweep angle at the 100% span position ispositive.
 18. The airfoil according to claim 13, wherein a leading edgesweep angle at the 0% span position is positive, and a leading edgesweep angle at the 100% span position is negative.
 19. The airfoilaccording to claim 1, wherein the leading edge dihedral at the 0% spanposition is in the range of −3° to −12°.
 20. The airfoil according toclaim 19, wherein the leading edge dihedral at the 0% span position isabout −4°.
 21. The airfoil according to claim 2, wherein the leadingedge dihedral at the 0% span position is about −10°.
 22. The airfoilaccording to claim 19, wherein the leading edge dihedral extends fromthe 0% span position to a 20% span position having a leading edgedihedral in a range of −2° to −6°.
 23. The airfoil according to claim22, wherein the leading edge dihedral includes a first point at a 75%span position and extends generally linearly from the first point to asecond point at the 85% span position.
 24. The airfoil according toclaim 19, wherein a maximum negative dihedral is in a range of 95-100%span position.
 25. The airfoil according to claim 24, wherein a leastnegative dihedral is in a range of 5-15% span position.
 26. The airfoilaccording to claim 19, wherein a maximum negative dihedral is in a rangeof 65-75% span position.
 27. The airfoil according to claim 26, whereina least negative dihedral is in a range of 0-10% span position.
 28. Theairfoil according to claim 19, wherein a maximum negative dihedral is ina range of 50-60% span position.
 29. The airfoil according to claim 1,wherein the airfoil is a fan blade for a gas turbine engine.
 30. Theairfoil according to claim 1, wherein the airfoil has a relationshipbetween a trailing edge dihedral and a span position, the trailing edgedihedral positive from the 0% span position to the 100% span position,wherein a positive dihedral corresponds to suction side-leaning, and anegative dihedral corresponds to pressure side-leaning.